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. 2023 Dec 15;18(12):e0295738.
doi: 10.1371/journal.pone.0295738. eCollection 2023.

Stream food webs in tropical mountains rely on allochthonous carbon regardless of land use

Alonso Ramírez  1 , Gabriela Vázquez  2 , Vinicio Sosa  2 , Pavel García  3   4 , Gonzalo Castillo  2 , José García-Franco  2 , Ma Luisa Martínez  2 , Klaus Mehltreter  2 , Eduardo Pineda  2 , M Susana Alvarado-Barrientos  2 , Federico Escobar  2 , Carolina Valdespino  2 , Adolfo Campos  2
Affiliations

Stream food webs in tropical mountains rely on allochthonous carbon regardless of land use

Alonso Ramírez et al. PLoS One. .

Abstract

The relative importance of allochthonous and autochthonous carbon (C) as sources of energy for tropical stream food webs remains an open question. Allochthonous C might be the main energy source for small and shaded forest streams, while autochthonous C is more likely to fuel food webs draining land uses with less dense vegetation. We studied food webs in cloud forest streams draining watersheds with forests, coffee plantations, and pastures. Our goal was to assess the effects of those land uses on the C source and structure of stream food webs. The study took place in tropical montane streams in La Antigua Watershed, in eastern Mexico. We selected three streams per land use and sampled biofilm and leaf litter as the main food resources, and macroinvertebrates and aquatic vertebrates from different trophic guilds. Samples were analyzed for δ13C and δ15N isotopes. Using a Bayesian mixing model, we estimated the proportional assimilation of autochthonous and allochthonous carbon by each guild. We found that consumers were mostly using allochthonous C in all streams, regardless of watershed land use. Our findings indicate that montane cloud forest streams are dominated by allochthony even in watersheds dominated by pastures. Abundant precipitation in this life zone might facilitate the movement of allochthonous C into streams. While food webs of streams from coffee plantations and pastures also rely on allochthonous resources, other impacts do result in important changes in stream functioning.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Sampling sites in the upper La Antigua watershed, Veracruz, Mexico.
The nine study streams were first or second order draining forest (green stars), coffee plantations (red pentagons), and pastures (yellow circles). Since we selected first to second order streams, not all symbols fall on a visible stream channel. Figure modified from Vázquez et al. (2023).
Fig 2
Fig 2. Principal Component Analysis (PCA) of study sites based on water physicochemistry.
Variables were measured at each end of the study reach and two points are representing each stream (points a and b). Numbers correspond to stream names in Table 2 and symbols to land uses, forest (green stars), coffee plantation (red pentagons), and pastures (yellow circles).
Fig 3
Fig 3. Biplots of resources and consumers under three land uses in the upper La Antigua, Mexico.
Error bars indicated 1 standard deviation. Resources are solid circles: Algae (blue), biofilm (green), and leaf litter (red). Consumers are corrected to account for trophic fractionation and are represented by open symbols: detritivores (triangles), herbivores (squares), omnivores (diamonds), and carnivores (circles).
Fig 4
Fig 4. Resource consumption by detritivores.
Posterior probability density of proportional source contributions by land use. The unshaded region corresponds to the 95% credible interval.
Fig 5
Fig 5. Resource consumption by herbivores (tadpoles).
Posterior probability density of proportional source contributions by land use. The unshaded region corresponds to the 95% credible interval.
Fig 6
Fig 6. Resource consumption by omnivores.
Posterior probability density of proportional source contributions by land use. The unshaded region corresponds to the 95% credible interval.
Fig 7
Fig 7. Resource consumption by carnivores.
Posterior probability density of proportional source contributions by land use. The unshaded region corresponds to the 95% credible interval.
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